The invention is based on a valve for controlling fluids of the type defined in greater detail in the preamble to claim 1.
In the industry, valves for controlling fluids are well known in which a valve closing member divides a low-pressure region in the valve from a high-pressure region, for instance in pumps or fuel injectors in motor vehicles.
European Patent Disclosure EP 0 477 400 A1 also describes such a valve, which is actuatable via a piezoelectric actuator and has an arrangement for a travel converter, acting in the direction of reciprocation, of the piezoelectric actuator; in this arrangement, the deflection of the actuator is transmitted via a hydraulic chamber, which functions as a hydraulic step-up means or coupling and tolerance compensating element. The hydraulic chamber encloses a common compensation volume between two pistons defining this chamber, of which one piston is embodied with a smaller diameter and is connected to a valve member to be triggered, and the other piston is embodied with a larger diameter and is connected to the piezoelectric actuator. The hydraulic chamber is fastened between the two pistons in such a way that the actuating piston executes a stroke that is increased by the step-up ratio of the piston diameter when the larger piston is moved a certain travel distance by the piezoelectric actuator. The valve member, piston and piezoelectric actuator are located on a common axis. Via the compensation volume of the hydraulic chamber, tolerances caused by temperature gradients in the component or different coefficients of thermal expansion of the materials used and possible settling effects can be compensated for without causing a change in position of the valve member to be triggered.
In the low-pressure region, in particular the hydraulic coupler, the hydraulic system requires a system pressure, which drops because of leakage if adequate refilling with hydraulic fluid is not done.
To that end, in the industry, for common rail injectors, versions are known in which the system pressure, which is expediently generated in the valve itself and which should be as constant as possible even upon system starting, is assured by delivery of hydraulic fluid from the high-pressure region of the fuel to be controlled into the low-pressure region having the system pressure. This is done with the aid of leakage gaps, which are defined by leakage or filling pins.
However, the dimensioning of the leakage gap is a problem; this gap must be adjusted such that the system pressure in the entire operating region can be built up and maintained on the low-pressure side of the valve. Upon temperature fluctuations of the fluid flowing through the leakage gap, the flow volume varies in accordance with the change in viscosity of the fluid. In common rail injectors, for instance, the leakage gap is chosen to be relatively large, so that the system pressure in the low-pressure region can be maintained even at extremely low temperatures, at which the viscosity of diesel fuel increases up to the point of gelling of the diesel fuel. As a result, at typical operating temperatures or high temperatures, a great amount of fluid passes through the gap around the leakage pin to reach the low-pressure region, and the excess amount of fluid must be bled off via a pressure holding valve. Thus an undesirably great leakage loss of the valve exists, and because of this the efficiency of the entire system drops sharply.
The object of the invention is to create a valve for controlling fluids in which a leakage quantity from a high-pressure region into a low-pressure region of the valve is at least approximately constant in the event of temperature changes.
The valve for controlling fluids of the invention having the characteristics of claim 1 has the advantage that the gap between the solid body and the valve body can be designed as relatively large, so that an adequate volumetric throughput is assured even at very low temperatures of the flowing fluid. At rising temperature and decreasing viscosity of the fluid flowing through the gap, the solid body expands more, because of its higher coefficient of thermal expansion, than does the material of the valve body, so that with increasing temperature the gap decreases in size, and thus advantageously the entire volumetric throughput is adjusted at medium and high temperatures in the same way as in the low temperature range.
Since with the valve of the invention an increase in the leakage rate in the low-pressure region as a consequence of rising temperatures is prevented, the necessity of bleeding off large amounts of excess pumped fluid through an overpressure valve is also dispensed with, and the efficiency of the entire system is therefore unimpaired.
Further advantages and advantageous features of the subject of the invention can be learned from the specification, drawing and claims.